Structure and Fluctuation of Proteins as Revealed by Compressibility

The adiabatic compressibility, <bata_s>，of 25 globular proteins in water was determined by means of sound velocity measurements at 25 C. Allthe proteins studied except for subtilisin and gelain showed positive <bata_s> values，indicating the large internal compressibility of the protein molecules the intrinsiccompressibility of proteins free from the hydration effect appeared to be comparable to that of正规ice.这些compressibility data were analyzed to examine the correlation of thecompressibility with some structural parameters and the amino acid compositions of proteins. It wasfound that <bata_s> increases with increasing partial specific volume and hydrophobicity ofproteins. The helix element also seemed to be a dynamic domain to increase <bata_s> . Four aminoacid residues (Leu, Glu, Phe, and His) greatly increased <bata_s>, and another four (Asn, Gly，ser,and Thr) decreased it. Some empirical equations were derived for the estimation of the < bat_s >values of unknown proteins on the basis of their amino acid compositions. the volume fluctuations ofproteins revealed by the compressibility data were in the range of 30-200 ml/mol，which corresponded to about 0.3% of the total protein volume. the conformational fluctuation seemedto enhance the thermal stability of proteins.它有时发现<bata_s> increases withincreasing the temperature and the glycerol concentration in solvent.这些results是ascribed todehydration of protein molecules。

The adiabatic compressibility, <bata_s> , of 25 globular proteins in water was determined by means of sound velocity measurements at 25゜C. All the proteins studied except for subtilisin and gelain showed positive <bata_s> values, indicating the large internal compressibility of the protein molecules. The intrinsic compressibility of proteins free from the hydration effect appeared to be comparable to that of normal ice. These compressibility data were analyzed to examine the correlation of the compressibility with some structural parameters and the amino acid compositions of proteins. It was found that <bata_s> increases with increasing partial specific volume and hydrophobicity of proteins. The helix element also seemed to be a dynamic domain to increase <bata_s> . Four amino acid residues (Leu, Glu, Phe, and His) greatly increased <bata_s> , and another four (Asn, Gly, Ser, and Thr) decreased it. Some empirical equations were derived for the estimation of the <bata_s> values of unknown proteins on the basis of their amino acid compositions. The volume fluctuations of proteins revealed by the compressibility data were in the range of 30-200 ml/mol, which corresponded to about 0.3% of the total protein volume. The conformational fluctuation seemed to enhance the thermal stability of proteins. It was also found that <bata_s> increases with increasing the temperature and the glycerol concentration in solvent. These results were ascribed to dehydration of protein molecules.